), 1963, Random Vibration: Vol. Unpredictable variations are what we mean by random. Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window), Click to share on LinkedIn (Opens in new window), Click to share on Pinterest (Opens in new window), Click to email this to a friend (Opens in new window), How To Choose The Right Vibration Test Lab. The manufacturer will simulate these vibrations on a shaker and operate their product under those conditions. More complex musical sounds arise from over-laying sine waves of varied frequencies simultaneously. Some common examples include an automobile riding on a rough road, wave height on the water, or the load induced on an airplane wing during flight. The form of a PSD plot defines the average acceleration of the random signal at any frequency. The PSD demonstrates how hard the shaker is working, but it doesn’t give any direct information regarding the forces experienced in the DUT. Aside from testing a product to identify and dwell at its resonance frequencies to ascertain fatigue life, you may also use sine testing to determine damage to equipment. Real-time data acquisition utilizes spectrum-averaging to create a statistical approximation of the vibration spectrum. What is Random Vibration Testing? ),1958, Random Vibration, New York: MIT Press/Wiley. Random vibration testing is, therefore, much more efficient and precise. Some of the more common random vibration test standards are MIL-STD-810, RTCA DO-160, and IEC 60068-2-64. Random Vibration. Canada East 18 Basaltic Road Concord, ON L4K 1G6, Canada West 8321 Coronet Rd, Edmonton AB T6E 4N7, US Shipping 4392 Broadway, Depew, NY 14043, USA, 905-738-0447 (Concord, ON) 416-939-0429 (Edmonton, AB), 18 Basaltic Road, Random vibration testing to failure can identify weaknesses and other design issues, allowing you to further refine your product. Generally, the random vibration spectrum profile is defined as a power spectral density (PSD) plot. The Random Vibration Control System provides precise, real-time, multi-channel control and analysis. Creating a Random Vibration Component Test Specification. The goals or uses of random vibration testingin industry usually is to evaluate the durability of the DUT and to check if a DUT will either work or fail under extreme conditions which it might be exposed to during its lifecycle. 12, 739-745. Among the many items typically tested with random vibration are … Recently, it has become feasible to record a long-time history and then play it back as a shake-test Control reference. Suppose that there were 1990 of them. [6][7][8] . Broad-spectrum random vibration contains not sinusoids but rather a continuum of vibrations.”, Would the totality be random? Mathematically, random vibration is characterized as an ergodic and stationary process. For the totality to be random, the amplitude and starting phase of each slice would have to vary randomly, unpredictably. Strike a tuning fork and the sound you will hear would be of a single sinusoidal wave produced at a specific frequency. Sine waves are necessary in other areas than music. Random-on-random tests superimpose narrow-band random noise on broadband random noise. For the totality to be random, the amplitude and starting phase of each slice would have to vary randomly, unpredictably. The most basic musical tones are sine waves at specific frequencies. Test specifications can be established from real environment measurements using an ASD envelope or a fatigue damage equivalence criterion (Extreme response spectrum and Fatigue damage spectrum). Such tests are claimed useful to simulate aircraft gunfire reactions. Difficulties encountered usually concentrate on the differences between sinusoidal vibration (sine testing) and random vibration testing. For instance, a manufacturer may want to see how their product may fail on account of various environmental vibrations it will probably encounter during its life. Random vibrations are seen in daily life scenarios (an automobile on a typical roadway, the firing of a rocket or an airplane wing in turbulent air flow) aren’t certainly repetitive or predictable like sinusoidal wave forms. Concord, ON, Canada L4K 1G6. These frequencies are vital to the vibration testing engineer, as they are the frequencies at which the DUT vibrates with the greatest amplitude and therefore, could be the most damaging to the DUT. Random vibration testing is usually the key testing technique for this type of application because all frequencies are exited at the same time hence creating more realistic representation of what occurs in the “real-world”. Every structure can vibrate and possess specific frequencies (resonance frequencies) wherein it vibrates using the greatest amplitude. Vibration Research pioneered such Field Data Replication (FDR) testing few years ago. Wayne Tustin’s had a good lay person’s description of random vibration: “I’ve heard people describe a continuous spectrum, say 10-2000 Hz, as 1990 sine waves 1 Hz apart. There is some confusion about the various tests available to the vibration testing engineer. The randomness is a characteristic of the excitation or input, not the mode shapes or natural frequencies. Test specifications can be established from real environment measurements using an ASD envelope or a fatigue damage equivalence criterion (Extreme response spectrum and Fatigue damage spectrum). Unpredictable variations are what we mean by random. The Grms value is typically used to express the overall energy of a particular random vibration event and is a statistical value used in mechanical engineering for structural design and analysis purposes. Back as a power spectral density ( PSD ) plot frequencies at which a device test... 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